The present invention relates to a printing ink or a printing varnish according to the preamble of the main claim as well as to its use for different printing methods.
Printing inks based on solid resins, in particular polycarbonate, are known from the prior art that are typically dissolved in halogen-free solvents. EP 0 688 839 B1 describes a printing ink of this type, acknowledged as category-defining, and is included in the present application with regard to the polycarbonate it describes as a possible embodiment of the binder belonging to the invention.
However, this printing ink known from the prior art is disadvantageous insofar as the solvent-containing printing inks known from the prior art tend to dry up in the screen as a result of evaporation of the solvent, in particular after a specific service life without printing. This therefore results in screen obstruction and additional cleaning is necessary. In the worst case scenario the sieve therefore becomes unusable. A further drawback of this technology known from the prior art is that the printing ink has to be dried using warm air in a tunnel dryer or kiln; processing is thus lengthened by the time required for drying and therefore cannot be optimised as desired. There is also an increased need for space and energy, which leads to a rise in costs, as a result of the IR dryer used for heat-drying.
A radiation-curable resin provided with reactive monomers that are also UV-curable is further known from the prior art. The related document GB 2 370 279 A describes a radiation-curing polyurethane acrylate with a polycarbonate component in the chemical structure, although it exhibits drawbacks with regard to workability. The problem of poor adhesion during ‘insert moulding’ processes, i.e. during the processing method in which a polycarbonate film printed using the printing ink is again insert moulded onto the printing face with a thermoplastic polymer, is particularly evident when printing on polycarbonate substrates. Since the ink lies between the polycarbonate film and injection moulding material, similar to a sandwich, the film cannot be rubbed off during daily use. A further drawback of this prior art is the adhesion to the mould during forming as well as the high sensitivity of the printed image to pressure and temperature, which in turn leads to detrimental washing out during insert moulding and consequently to a poor printed image.